Impact of Parasites on the Immune System of Cattle

Abstract

All cattle have parasites. Even low worms burdens, often considered normal, can have an economic impact on productivity. The major effects of parasitism are not from competition for host nutrition, but rather from phenomenon such as damage to host tissues, alteration of physiological functions, host reaction to the parasites, and adverse immune interactions. Consequences of the interactions between the host immune system and parasites can be dramatic. In order to survive in immunocompetent hosts, parasites either modulate or avoid the host immune responses. When parasites actively modulate host immunity, the results can range from the inapparent to severe pathologic changes that compromise the heal th and survival of the animal. The majority of these changes have some adverse effects on productivity. Suppression of host immune responses can increase susceptibility to other parasites as well as bacteria and viruses. Parasite-induced suppression of host immune systems may reduce responses to vaccines, which can be misinterpreted as vaccine failure. A practical consequence of the immune response to parasites is the production of antibodies that can be detected by various techniques. The complex immune interactions and a wide diversity of parasite transmission patterns require more than a cursory consideration to achieve maximum production efficiency. The astute bovine practitioner must consider the overall parasite-host interface in order to develop a more integrated approach to herd health programs.